Priority is claimed from Republic of Korean Patent Application No. 99-60557 filed Dec. 22, 1999, which is incorporated in its entirety by reference.
1. Field of the Invention
The invention relates generally to a method of forming a gate electrode in a semiconductor device. More particularly, the present invention relates to a method of forming a gate electrode in a semiconductor device by which (TiO2)x(Al2O3)1-x, wherein x has a value ranging from approximately 0.05 to approximately 0.85, in which a titanium oxide film (TiO2) having a high dielectric constant and leakage characteristic and an aluminum oxide film having a good interfacial property are mixed, is used as a gate insulating film.
2. Description of the Prior Art
In a semiconductor device such as DRAM, logic, etc. that has been mass-produced presently, a silicon oxide film (SiO2) grown by thermal process or a rapid thermal process is mainly used as a gate insulating layer. As the design rule is scaled downed, however, the thickness of the silicon oxide film is scaled down below approximately 25 to approximately 30 A being a limit to the tunneling. Thus, it is expected that the gate insulating film of 0.1 xcexcm technology will result in approximately 15 to approximately 20 A in thickness. Due to the off current increased by direct tunneling, however, there is a possibility that it may adversely affect the operation of a device. Particularly, in case of a memory device, every effort to reduce the leakage current has been made. Recently, as a result of these efforts, many researches into attempt to adopt an insulating material having a high dielectric constant as a gate insulting film have been carried out. Among them, a research by which an tantalum oxide film (Ta2O5) used as a dielectric film of a capacitor is used as a gate insulating film had been mostly actively carried out. However, if the tantalum oxide film is used as the gate insulating film and a polysilicon film is used as the gate electrode, due to reaction between the tantalum oxide film and the polysilicon film in an interface between the tantalum oxide film and the polysilicon oxide film, a silicon oxide film is formed, resulting in increase in the thickness of the entire oxide film. At this time, in order to prevent this reaction, a metal structure of a barrier metal layer such as TiN and tungsten may be used. In this case, however, as variations such as the threshold voltage shift, etc. are caused, various types of optimization such as counter doping within a channel, etc. are required. Therefore, it is found that there is a limit to applying the conventional technology.
On the other hand, it was found that a dielectric film or a gate insulating film of a capacitor using an aluminum oxide film (Al2O3), that has been recently researched actively, has a good leakage current characteristic of  less than 10-9A/cm2 and a god interfacial property (Dit less than 1xc3x971011eVxe2x88x921 cmxe2x88x921). Also, it shows a preferred effect and a stable characteristic during process at high temperature. Meanwhile, in case of a titanium oxide film (TiO2) having a dielectric constant of about 25 about 3 5, it has a high dielectric constant, but has a drawback that it has a high leakage current since bulk traps or interface defects within a thin film are great.
In order to accomplish the above object, a method of forming a gate electrode in a semiconductor device according to the present invention is characterized in that it comprises the steps of forming a (TiO2)x(Al2O3)1-x film on a semiconductor substrate, forming a conductive film on the entire structure and patterning the conductive film and the (TiO2)x(Al2O3)1-x film to form a gate electrode.